1. Technical Field
The present invention relates generally to torque management in an automatic transmission primarily intended for motor vehicle use, and more particularly, to a method of adapting to the K-factor value of a torque convertor and providing adaptive stall-torque management for the automatic transmission.
2. Discussion
Generally speaking, a power train is composed of two parts, a power plant such as an internal combustion engine, and some means of transferring the power to the ground to propel the vehicle, which is typically some sort of transmission. Engine torque and speed are converted in the transmission generally in accordance with the tractive-power demand of the vehicle. Automatic transmissions are designed to take control of frictional units, gear ratio selection and gear shifting for effecting gear changes in the transmission. One advanced form of transmission control system has been proposed which would offer the possibility of enabling the automatic transmission to adapt itself to changing conditions and the torque management system to adapt to part-to-part variation. An example of such an electronic controlled automatic transmission system is disclosed in U.S. Pat. No. 4,875,391, entitled "An Electronically-Controlled, Adaptive Automatic Transmission System", issued to Leising et al. One feature of the above-identified patented automatic transmission system is a method of stall torque management which issued into corresponding U.S. Pat. No. 4,991,097, entitled "Method Of Stall Torque Management For An Electronic Automatic Transmission System", to Davis et al. The aforementioned issued patents are hereby incorporated by reference. The patented stall-torque management method disclosed in the above-identified patent reduces the speed of the engine and hence the torque out of the torque converter, reducing the torque into the automatic transmission in response to predetermined conditions existing in the transmission.
The above-identified methods of stall-torque management have worked well to reduce input power from the engine during a stall to improve differential durability. However, known torque management methodologies typically take into consideration an established K-factor value that serves as an indication of a value which will suffice for a certain percentile of all the torque converters that are available. The K-factor of a torque converter has been defined as the engine speed in revolutions-per-minute (RPM) divided by the square root of the engine torque output. The K-factor value therefore provides a relative indication of the efficiency of the torque converter. In the past, torque management control utilized an established K-factor, which was usually established based on test data accumulated from sampled torque converters. However, the actual K-factor value varies among individual torque converters, because there are usually manufacturing variations. For example, torque converters established with a 180K nominal K-factor value may vary from 145K to 215K, depending on manufacturing quality. By assuming the established nominal K-factor value, variance in actual performance results. If the torque management manages to a 90th percentile torque converter, 90% of vehicles equipped with the torque converters may be over-managed, while the remaining 10% of vehicles equipped with torque converters may be under-managed. In addition, the K-factor for a given torque converter may vary over time due to wear and tear of the torque converters. Known approaches have not adapted to changes which may occur in an individual torque converter over time.
It is, therefore, one object of the present invention to provide for a method of providing enhanced torque management in an automatic transmission by adapting to the characteristics of an individual torque converter.
It is another object of the present invention to provide for an improved method of adaptively determining the K-factor of a torque converter and managing engine speed to obtain a managed torque from the automatic transmission.
It is yet another object of the present invention to provide for an adaptive K-factor for individual torque converters, which takes into consideration differences amongst a plurality of torque converters and changes to an individual torque converter that may occur over time, such that torque can be managed to prevent transmission components from breaking, while ensuring adequate performance of the vehicle.